The following poly(aryl ether sulfone) polymers are commercially available. Victrex polyethersulfone (made by Imperial Chemical Industries PLC) contains repeating units of the following formula: ##STR1## Udel polysulfone (made by Union Carbide Corporation) contains repeating units of the following formula: ##STR2##
These poly(aryl ether sulfones) have a wide variety of end-use applications, including use in coatings and for casting into films. Film made from these poly(aryl ether sulfones) have a good combination of physical properties. However, the lack of low cost, low boiling and commercially available solvents for these polymers limits their use in films.
Since methylene chloride is an excellent solvent and widely employed commercially, there has been a desire to prepare solutions of poly(aryl ether sulfones) in methylene chloride for film applications. Such solutions, however, must be stable over long periods of time, i.e., have long shelf-life.
The problems which exist with poly(aryl ether sulfones) solutions in solvents such as methylene chloride have been succinctly summarized in U.S. Pat. No. 3,875,103 (column 1, lines 11 to 19) as follows:
"Solutions of thermoplastic amorphous aromatic polysulphones have hitherto suffered from instability leading to solutions having a short shelf-life. Such solvents are chlorinated hydrocarbons such as methylene chloride, chloroform, 1,1,2-trichloethane, and 1,2-dichloroethane. Alternatively, solvents which give solutions of the polysulphones having long shelf life have high boiling points, and are therefore difficult to remove." PA0 bisphenol-A PA0 hydroquinone PA0 dihydroxy diphenyl sulfone PA0 biphenol PA0 4,4'-dichloro or 4,4'-dinitro PA0 diphenyl sulfone.
It is known that poly(aryl ether sulfone) (I) precipitates out of a methylene chloride solution. When poly(aryl ether sulfone) (II) is dissolved in methylene chloride a precipitate forms (it takes several weeks) which must be filtered out if homogeneous films are to be prepared.
Thus, a new poly(aryl ether sulfone) was needed which would dissolve in solvents such as methylene chloride and remain in solution for extended periods of time. Such a poly(aryl ether sulfone) is described in U.S. patent application Ser. No. 536,843 filed Sept. 29, 1983 in the names of L. M. Robeson et al, titled "Polyarylethersulfone Polymer Solution" (commonly assigned). This application describes solutions for coating compositions comprising select polyarylethersulfones dissolved in methylene chloride or N,N-dimethyl formamide. The following poly(aryl ether sulfone) is specifically depicted in Ser. No. 536,843: ##STR3## This poly(aryl ether sulfone) was found to dissolve in methylene chloride and remain totally dissolved therein even after two months.
However, it recently has come to light that methylene chloride has potential toxicity problems (see for example, Chemical Week, "Methylene Chloride in Limbo", May 8, 1985). Thus, it should be highly desirable to replace methylene chloride with another commonly available, non-toxic and low boiling solvent. Cyclohexanone has been found in this invention to be such a solvent.
In the following U.S. Patents solutions of poly(aryl ether sulfones) are described:
U.S. Pat. No. 3,875,103 describes a solution for coating comprising at least one thermoplastic amorphous aromatic polysulfone dissolved in a solvent mixture comprising: (a) 70 to 85% by volume of a mixture of (i) at least one cyclic aliphatic ketone having a ring containing 5 to 7 carbon atoms and having a boiling point, at atmospheric pressure, of less than 200.degree. C. and (ii) at least one inert liquid compound containing a polar group selected from --SO--, --SO.sub.2 --, --CO, N and N-- groups and having a boiling point, at atmospheric pressure, of less than 210.degree. C., the cyclic aliphatic ketone to inert liquid compound volume ratio being 70:30 to 95:5, and (b) 30 to 15% by volume of at least one dialkyl ketone having a boiling point, at atmospheric pressure, of less than 150.degree. C., the concentration of the polysulphone being 5 to 25 g in 100 cm.sup.3 of solvent mixture.
In the sole example of this patent, a poly(aryl ether sulfone) corresponding to structural formula (I), depicted above, is dissolved in a mixture of cyclohexanone and dimethyl sulphoxide at 80.degree. C. to form a solution. The solution is cooled to 50.degree. C. and methyl ketone is added. Thus, three different solvents are required to prepare the poly(aryl ether sulfone) solution.
U.S. Pat. No. 3,993,843 describes an aqueous dispersion of a polysulfone resin. The dispersion is described as containing 10-60% by weight of a film forming binder which is an aromatic polysulfone resin dispersed in 37-89.9% by weight of water. The dispersed binder particles have a particle size of about 0.02-0.5 microns and are dispersed by about 0.1-3.0% by weight of a surfactant. The patent also describes a process for preparing an aqueous dispersion from an aromatic polysulfone resin. In this process, the polysulfone resin is dissolved in a water miscible solvent such as methylene chloride, tetrahydrofuran, cyclohexane, dimethyl formamide, or dimethyl acetamide to form a solution having a polymer solids content of about 10-30% by weight. The solution is then diluted with a water immiscible solvent such as toluene, xylene and trichlomethylene to a 2-9% polymer solids content. This solution is then added, under high shear mixing conditions, to a solution of 95-99% by weight of water and 1-5% by weight of a nonionic or anionic surfactant to form an emulsion.
In example 1 of U.S. Pat. No. 3,983,843, the poly(aryl ether sulfone) structurally depicted as (II) above is dissolved in methylene chloride and heated for one hour to form a solution. This solution is then mixed with acetone, toluene and methylene chloride to form portion 2. Portion 2 contains water and surfactant. Portion 1 is added to Portion 2 under high shear mixing conditions to form an emulsion. This patent does not disclose the poly(aryl ether sulfones) of this invention nor the use of cyclohexanone as a solvent.